1. Field of the Invention
The present invention relates to an air suspension system, particularly in which an air chamber has a variable volume so as to provide different spring constants.
2. Description of Prior Art
It is well known to include a variable volume air chamber in an air suspension system to provide different spring constants. In such an air suspension system, an air chamber serves as an air spring and is defined at the upper end of a piston rod which in turn, forms a shock absorber. Another air chamber is defined around the air chamber. A valve rod is driven for rotation by a motor so as to selectively communicate between the two air chambers to change the air spring constant (see, for example, Japanese laid-open patent publication No. 80920/85).
However, such a conventional air suspension system can provide only two different air spring constants. Riding comfort and maneuverability are far from satisfactory as such.
In order to improve the riding confort and maneuverability of a vehicle, it is desirable to finely control the spring constant of an air suspension system in response to travelling conditions of a vehicle.
When an air suspension system has a plurality of spring constants, it is desirable to reduce the size of the overall suspension by simplifying a mechanism to vary the spring constants. This facilitates mounting of the suspension to a vehicle.
It is also necessary to improve the response when the spring constants are changed. This is due to the fact that an optimum spring constant cannot be obtained in response to travelling conditions of a vehicle if the spring constants are not changed quickly. Riding comfort and maneuverability can not be improved as such.